<h2>DESCRIPTION</h2>

<em>v.out.vtk</em> 
converts a GRASS vector map in binary format to the VTK ASCII 
output. 
<p>If the <b>output</b> parameter is not given, the output will be send to stdout.

<h2>NOTES</h2>

The following vector types can be exported together in one VTK ascii file:
<ul>
	<li>point</li>
	<li>line</li>
	<li>centroid</li>
	<li>boundary</li>
	<li>area</li>
	<li>face</li>
</ul>

Category data (cat) for the selected vector type and layer will be written as scalar
data with name "cat_{vectorname}". If no cat exists, the value will set to -1 as normal cat's are
always positive.
If a vector has more categories in one layer, only the first category
will be exported.
<br>
<br>
3d vectors are supported by default. The created VTK data always includes x, y and z coordinates 
(z = 0 if not a 3d vector map).
Note that you can easily convert your 2d vectors into 3d vectors with v.drape.
<br>
<br>
Because of the 32bit limits of OpenGL which is used by VTK, visualisation errors may occur if
the grass region contains coordinates greater than 1.000.000 and vector coordinates
with 0.01 - 0.001 meters precisison. For this reason, the flag "-c" was added. The coordinates are 
transformed to smaller coordinates (by decreasing the coordinates with the region center).
<br>
<br>
If the "-c" flag is used and the data should be visualised together with other data exported via *.out.vtk
modules, be sure the "-c" flag was also set in these modules. 
But this will only work with data from the SAME location 
(The reference point for the coordinates transformation is based on the default region).
<br>
<br>
The GRASS vector data is converted into the polydata format of VTK: 

<ul>
 <li><i>vtk Vertices</i> -- representing points and centroids </li>
 <li><i>vtk lines</i> -- representing lines and boundaries </li> 
 <li><i>vtk polygons</i> -- representing areas and faces </li>
</ul>
<p>The VTK file can be visualized with
<em><a href="http://www.vtk.org">VTK Toolkit</a></em>,
<em><a href="http://www.paraview.org">Paraview</a></em> and
<em><a href="http://mayavi.sourceforge.net">MayaVi</a></em>.

<h3>Attention</h3>
<p>If areas or faces are exported, the data have to be triangulated within Paraview or
MayaVi.


<h2>EXAMPLE</h2>

Spearfish example:
<p>Export the soils with cats in layer 1:
<div class="code"><pre>
v.out.vtk input=soils type=area layer=1 output=/tmp/soils.vtk
</pre></div>
Export the streams with cats in layer 1:
<div class="code"><pre>
v.out.vtk input=streams type=line layer=1 output=/tmp/streams.vtk
</pre></div>
Write the archsite vtk output to stdout with cats in layer 1:
<div class="code"><pre>
v.out.vtk input=archsites type=point layer=1
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="v.out.ascii.html">v.out.ascii</a><br>
<a href="r.out.vtk.html">r.out.vtk</a><br>
<a href="r3.out.vtk.html">r3.out.vtk</a><br>
</em>


<h2>AUTHOR</h2>

Soeren Gebbert

<!--
<p>
<i>Last changed: $Date$</i>
-->
